Fedirchuk B, Hochman S, Shefchyk S J
Department of Medicine, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Exp Brain Res. 1992;89(3):511-6. doi: 10.1007/BF00229875.
The external urethral sphincter (EUS) and external anal sphincter (EAS) are striated muscles that function to maintain urinary and fecal continence respectively. This study examines the short-latency synaptic input from a variety of cutaneous perineal and muscle/cutaneous hindlimb afferents to the motoneurons innervating these muscles. Intracellular recordings from antidromically identified EUS and EAS motoneurons provided records of the postsynaptic potentials (PSPs) produced by electrical stimulation of peripheral afferents in decerebrate or chloralose anesthetized cats. Excitatory postsynaptic potentials (EPSPs) were produced in most EUS and EAS motoneurons by stimulation of ipsilateral and contralateral sensory pudendal (SPud) and superficial perineal (SPeri) cutaneous nerves. The shortest central latencies in the study (1.5 ms) suggest that there are disynaptic excitatory, in addition to tri- and oligosynaptic, connections within these reflex pathways. EPSPs mixed with longer latency inhibitory potentials (E/I PSPs) were observed in both motoneuron populations, but were found more frequently in EAS motoneurons. These E/I PSPs were evoked more often from contralateral afferents than from ipsilateral afferents. Cutaneous nerves innervating the hindlimb had weaker if any synaptic effects on sphincter motoneurons. Stimulation of ipsilateral hindlimb muscle nerves rarely produced PSPs in EUS motoneurons and had weak synaptic actions on EAS motoneurons. In 2 of 22 animals (both decerebrate), large inhibitory potentials predominated over early small EPSPs suggesting that inhibitory pathways from these afferents to sphincter motoneurons can be released under certain circumstances. The relation between the segmental afferents to EUS and EAS motoneurons and the neural circuitry influencing them during micturition and defecation are discussed.
尿道外括约肌（EUS）和肛门外括约肌（EAS）是横纹肌，分别起到维持尿失禁和大便失禁的作用。本研究考察了来自会阴区各种皮肤及肌肉/皮肤后肢传入神经对支配这些肌肉的运动神经元的短潜伏期突触输入。对经逆向鉴定的EUS和EAS运动神经元进行细胞内记录，得到了在去大脑或水合氯醛麻醉的猫中电刺激外周传入神经所产生的突触后电位（PSP）记录。刺激同侧和对侧的阴部感觉（SPud）神经和会阴浅（SPeri）皮神经，在大多数EUS和EAS运动神经元中产生兴奋性突触后电位（EPSP）。该研究中最短的中枢潜伏期（1.5毫秒）表明，除了三突触和少突触连接外，这些反射通路中还存在双突触兴奋性连接。在两个运动神经元群体中均观察到EPSP与潜伏期更长的抑制性电位混合（E/I PSP），但在EAS运动神经元中更常见。这些E/I PSP由对侧传入神经诱发的频率高于同侧传入神经。支配后肢的皮神经对括约肌运动神经元的突触作用较弱（若有）。刺激同侧后肢肌肉神经在EUS运动神经元中很少产生PSP，对EAS运动神经元的突触作用较弱。在22只动物中的2只（均为去大脑动物）中，大的抑制性电位占主导，超过早期小的EPSP，这表明在某些情况下，从这些传入神经到括约肌运动神经元的抑制通路可以被释放。本文讨论了EUS和EAS运动神经元的节段性传入神经与在排尿和排便过程中影响它们的神经回路之间的关系。
